The present invention relates to shock absorbers and more particularly to shock absorbers employing acceleration controlled vortex throttles.
The suspension system of a wheeled vehicle has two fundamental goals. They are: first to protect the payload from excessive acceleration, excessive velocities and excessive displacements, and second to keep the wheel in contact with the ground so as to retain controllability of the vehicle as it traverses the terrain. Springs provide a suspension force level dependent upon relative position of wheel and vehicle body.
A shock absorber is a device placed between the axle and vehicle body, designed to absorb energy of relative motion between the axle and vehicle body. Ideally, it should consider motion relative to an earth reference for the vehicle body, and motion relative to the terrain surface for the wheel. The shock absorber must then dissipate the energy of relative motion to the surrounding environment so that the shock absorber does not over-heat and self-destruct.
Most current shock absorbers are piston-cylinder arrangements using hydraulic fluid as a working medium. The hydraulic fluid is forced through an orifice and in going through the orifice is accelerated to a high velocity and stores kinetic energy. When the fluid exits from the orifice, it dissipates its kinetic energy through turbulence into heat which results in a higher temperature for the hydraulic fluid. This heat is dissipated by conduction and convection to the surrounding air for a conventional vehicle. To permit some decision on the part of the shock absorber as to how much of a resisting force it is going to develop or how much energy it is going to absorb, and to permit it to absorb different amounts for compression and rebound, one orifice is used for compression and another orifice is used for rebound.
One of the problems with a simple orifice is that the force developed varies as the square of the rate at which the shock is changing length in that this length is proportional to the velocity with which fluid is forced through the orifice. This means that the shock is soft or low velocities and hard for higher velocities. It is desirable that this not occur. For that reason, more sophisticated valving systems have been developed which permit the area of the orifice to change so as to accommodate the higher pressures associated with high shock velocities.
The major problem with the conventional shock absorber is it has very limited input information. By examining the internal hydraulic pressure, it reaches a conclusion as to the rate of closing or rate of extension of the shock absorber and based on this information, adjusts its damping coefficient accordingly. As a consequence, the shock absorber system has a very limited intelligence. Of necessity, therefore, its damping characteristics are selected as a fixed compromise. This compromise considers the total exposure anticipated within the terrain-vehicle-speed operating envelope.
Selection of the best shock absorber system for a new vehicle is approximated at the drawing board, but selection is finalized by an expert who rides in the vehicle and makes judgements of modification to achieve his optimum compromise of shock ratio, nose angle and degree of control for each of the various stages of shock absorber valving, etc. Consequently, conventional shock absorbers usually operate in an off-design point condition.
There are three major problem areas which remain unsolved as a result of the limited information that is currently available in conventional shock absorbers and the method of operation which is forced upon it by its current limited information processing capability. There are: (1) The unit absorbs more energy than is necessary and this sometimes leads to catastrophic failure of the unit; (2) The unit applies a less than optimum forcing function to the vehicle; (3) The wheel ground-contact time integral is decreased. This has an adverse influence on vehicle dynamics. It limits the vehicle terrain speed performance which is truly usable and thus limits system effectiveness.